The present invention is directed at a grease having desirable properties over wide temperature ranges.
Adequate lubrication of outdoor equipment, such as heavy production, construction, or mining equipment, may be hampered for a variety of reasons. The bearings and gears of such equipment frequently must operate under high, or shock, load conditions, at slow speeds, and in the presence of sand or other abrasive materials. Greases used under such conditions must contain oils of relatively high viscosity at normal operating temperatures to prevent damage to the moving parts because the thickness of the protective lubricant film increases as oil viscosity and sliding speed increase, and decreases directionally with applied load. Clearly, the lubricating film thickness needs to be greater than the diameter of abrasive particles if adequate protection to bearing and gear surfaces is to be provided. Furthermore, greases used in such dusty environments need to resist slumping at high ambient summer temperatures in order to maintain adequate sealing capabilities around the shafts of bearings and gears in order to prevent the ingress of dirt and abrasive materials. Thus, good performance greases for these applications need to have a moderately firm consistency, as well as a relatively high oil viscosity for summer operating conditions.
Automatic lubricating systems used in such heavy equipment frequently involve the use of long, relatively small diameter tubes to deliver the grease from a central supply location to the bearing or gear to be lubricated. While this normally presents no problem at ambient summer temperatures, ability to deliver the grease through these lines to the lubricated parts at winter ambient temperatures is often the limiting factor in grease selection. The National Lubricating Grease Institute has developed a series of nomographs by which dispensibility can be calculated from a number of factors which include tube length, tube diameter, pumping pressure, and grease apparent viscosity. It is well known in the art that grease apparent viscosity is a function primarily of base oil viscosity and grease consistency, at the dispensing temperature. Hence, in sub-arctic regions where ambient temperatures may vary from as low as -40.degree. C. in winter to as high as 35.degree. C. in summer, conflicting demands are placed on grease properties. In winter a low base oil viscosity and soft consistency is preferred for good dispensibility, while, in summer, relatively high viscosity and firm consistency is preferred to provide adequate lubrication and sealing against the ingress of dirt and abrasive materials.
U.S. Pat. No. 3,813,338 discloses a lubricant for use in textile machines comprising a naphthenic base oil, 0.3-6 wt.% polyolefin as a tackiness agent and 0.1-1.5 wt.% lithium soap.
U.S. Pat. No. 4,075,112 and U.S. Pat. No. 4,075,113 disclose grease compositions comprising 2-15 wt.% aluminum soap, 25 to 97% of a hydrogenated or non-hydrogenated polymer of a monoolefinic hydrocarbon having 4 carbon atoms and a mean molecular weight of between 300 and 2500, and 0-60 wt.% of a lubricating oil, which preferably is a mineral oil.
Japanese Patent Publication No. J5-9,109,595 discloses a lithium soap which may include a refined base stock derived from naphthenic, paraffinic and mixed base crudes. Synthetic lubricating oils also are disclosed as being useful. These synthetic oils include polymers and copolymers of alpha olefins.
Japanese Patent Publications J5-9,142,291-3 disclose lithium-containing lubricants comprising an aliphatic hydrocarbon oil.
Japanese Patent Publication No. J5-8,122,996 discloses a grease composition having lithium thickener and a base oil comprising substantially a C.sub.19 -C.sub.30 naphthenic hydrocarbon.
U.S. Pat. No. 3,112,270 discloses a grease comprising a mineral oil, ethylene polymer and a soap thickener.
U.S. Pat. No. 3,114,708 discloses the manufacture of a dry grease blend comprising 20 to 75 weight percent polyolefin.
U.S. Pat. No. 3,813,338 discloses a high retention thickened oil lubricant for textile machinery comprising a naphthenic base oil, a polyolefin and a lithium thickener.
U.S. Pat. No. 3,539,512 discloses the combination of a base oil and a polyolefin thickener to produce a grease having a low tendency to bleed.
U.S. Pat. No. 3,541,011 discloses a gel lubricant comprising a mineral oil and polyethylene thickener.
U.S. Pat. No. 4,406,800 discloses a grease useful over a wide temperature range comprising a polyalphaolefin base fluid and a thickener.
It would be advantageous to provide a grease having acceptable dispensing and lubricating properties over a wide temperature range.
It also would be desirable to provide a grease having a high oil viscosity and relatively firm consistency in warm weather and a relatively soft consistency and relatively low apparent viscosity for pumping in cold weather.
It also would be desirable to provide a grease which is relatively inexpensive to manufacture, is shear stable, resists slumping, and has good extreme pressure and anti-wear properties.